1. Field of the Invention
The present invention relates to a headlamp that is provided to a vehicle such as an automobile, and has a projection optical system such as a projector lens, and more particularly to a headlamp that eases an illumination change in the vicinity of a cut line formed at a front end (upper end) of a light distribution pattern for glare proof.
2. Description of Related Art
There has been known, as a headlamp for a vehicle such as an automobile, a projector-type headlamp that converges a light beam from a bulb, serving as a light source, with a convergent reflector and projects the light beam forward by using a projection lens.
In a light distribution on pattern for passing by an oncoming vehicle (low beam) for preventing glare to the oncoming vehicle, the aforementioned projector-type headlamp is provided with a shade that blocks a part of a light beam at the rear of the projection lens in order to form a desired cut line for cutting a light flux at the side of an opposite lane.
It has been proposed that a parabolic reflector that reflects a light beam emitted from the same light source so as to irradiate a portion ahead the vehicle is added to the projector-type headlamp.
As a conventional technique relating to the headlamp using both the projection optical system and the parabolic reflector described above, for example, Japanese Patent Application Laid-Open (JP-A) No. 2010-153333 describes a vehicle headlamp that guides a part of a light beam emitted from a light source to an auxiliary reflector, which is provided diagonally backward above a projection lens, and irradiates the same in front of the vehicle from the auxiliary reflector without passing through the projection lens as a high-beam spot light. In the technique described in the JP-A No. 2010-153333, a cut line in a low beam is formed by blocking a part of light incident on the projection lens by an edge of a shade arranged at the rear of the projection lens.
JP-A No. 2010-123404 describes a vehicle headlamp that guides a part of a light beam emitted from a light source to an additional reflector provided diagonally backward below a projection lens, and irradiates the same from the additional reflector with a light distribution pattern spreading in the lateral direction below a cut-off line.
In the technique described in the JP-A No. 2010-123404, a cut line is formed by a movable shade provided in the vicinity of a rear-side focal point of a projection lens.
In a general projector-type headlamp in which a portion ahead a vehicle is irradiated only by a projection optical system, and a cut line is formed by a shade arranged backward of the projection lens, illumination intensity sharply changes in the vicinity of the cut line, whereby contrast increases.
In the JP-A Nos, 2010-153333 and 2010-123404 described above, the out line in a low beam is formed by the shade provided to the projection optical system, the property described above is similarly applied thereto.
When an optical axis is changed clue to vehicle pitching, etc., a range that can be visually confirmed by a driver sharply changes, which might confuse the driver.
It is supposed that a driver goes back and forth between a country where drivers keep to the right side of the road and a country where drivers keep to the left side of the road. In this case, a reflector-type headlamp can easily prevent glare to an oncoming vehicle by attaching a seal-type light shielding member to an outer lens. However, this measure cannot be applied to a projector-type headlamp. Therefore, it is necessary to suppress a light distribution to a distance or to add a unit for changing the shade that forms the cut line and the like in order to prevent glare in either of left-hand traffic and right-hand traffic.
When a high-intensity discharge (HID) bulb, which has recently been increasingly used, is used as a light source, a light-emitting portion is relatively large, and its outer edge is not clear, unlike a halogen bulb that is relatively close to a point light, source because only a filament emits light. Therefore, in order to satisfactorily form a cut line on a projector-type headlamp, a light-shielding pattern having a shape of a stripe has to be provided on the surface of the bulb, resulting in that efficiency is deteriorated due to a loss of light flux.